Fluid pressure booster

ABSTRACT

A fluid pressure booster includes: a control piston in which brake operation input acts in an advancing direction, and reaction based on fluid pressure of a booster fluid pressure generation chamber that generates fluid pressure for actuating a master piston acts in a retracting direction; a pressure increasing valve provided between the booster fluid pressure generation chamber and a fluid pressure generation source so as to open at the time of advance of the control piston and close at the time of retraction of the control piston; and a pressure reducing valve provided between a release chamber and the booster fluid pressure generation chamber so as to close at the time of the advance of the control piston and open at the time of the retraction of the control piston. The pressure increasing valve includes first valve means and second valve means that sequentially open according to an increase in the brake operation input, and a seal diameter of the second valve means is larger than that of the first valve means. Thus, it is possible to enhance initial response of the pressure increasing valve, and also enhance response of the pressure increasing valve when a brake operation member is strongly operated.

RELATED APPLICATION DATA

The present invention is based upon Japanese priority application No.2005-105123, which is hereby incorporated in its entirety herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fluid pressure booster including: acontrol piston in which brake operation input from a brake operationmember acts in an advancing direction, and reaction based on fluidpressure of a booster fluid pressure generation chamber that generatesfluid pressure for actuating a master piston of a master cylinder actsin a retracting direction; a pressure increasing valve provided betweenthe booster fluid pressure generation chamber and a fluid pressuregeneration source so as to open at the time of advance of the controlpiston and close at the time of retraction of the control piston; and apressure reducing valve provided between a release chamber communicatingwith a reservoir and the booster fluid pressure generation chamber so asto close at the time of the advance of the control piston and open atthe time of the retraction of the control piston, the control pistonbeing actuated forward and backward so that the brake operation inputand the reaction based on the fluid pressure in the booster fluidpressure generation chamber are balanced to regulate the fluid pressurein the fluid pressure generation source to act on the booster fluidpressure generation chamber.

2. Description of the Related Art

Such a fluid pressure booster has been known from, for example, JapanesePatent Application Laid-Open No. 2002-308085.

In such a fluid pressure booster, an activation load (a force requiredfor opening a valve) of the pressure increasing valve is reduced bysetting a small seal diameter. Such setting of the seal diameter,however, reduces response when a brake operation member is stronglyoperated to introduce high fluid pressure from a fluid pressuregeneration source into a booster fluid pressure generation chamber.Further, setting a large seal diameter to the contrary increases theactivation load of the pressure increasing valve.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the above-mentionedcircumstances, and has an object to provide a fluid pressure boosterthat enhances initial response of the pressure increasing valve and alsoenhances response of the pressure increasing valve when a brakeoperation member is strongly operated.

In order to achieve the above object, according to a first feature ofthe present invention, there is provided a fluid pressure boostercomprising: a control piston in which brake operation input from a brakeoperation member acts in an advancing direction, and reaction based onfluid pressure of a booster fluid pressure generation chamber thatgenerates fluid pressure for actuating a master piston of a mastercylinder acts in a retracting direction; a pressure increasing valveprovided between the booster fluid pressure generation chamber and afluid pressure generation source so as to open at the time of advance ofthe control piston and close at the time of retraction of the controlpiston; and a pressure reducing valve provided between a release chambercommunicating with a reservoir and the booster fluid pressure generationchamber so as to close at the time of the advance of the control pistonand open at the time of the retraction of the control piston, thecontrol piston being actuated forward and backward so that the brakeoperation input and the reaction based on the fluid pressure in thebooster fluid pressure generation chamber are balanced to regulate thefluid pressure in the fluid pressure generation source to act on thebooster fluid pressure generation chamber, wherein the pressureincreasing valve includes first valve means and second valve means thatsequentially open according to an increase in the brake operation input,and a seal diameter of the second valve means is larger than that of thefirst valve means.

With the first feature of the present invention, the pressure increasingvalve includes the first and second valve means, and according to theincrease in the brake operation input by the brake operation member, thefirst valve means having the relatively small seal diameter opens andthen the second valve means having the relatively large seal diameteropens. Thus, initial response can be ensured by opening the first valvemeans having a small activation load in an early stage of brakeoperation requiring small brake operation input, and response can beincreased by opening both the first and second valve means when thebrake operation member is strongly operated, thereby allowing theincrease in the initial response of the pressure increasing valve, andalso the increase in the response of the pressure increasing valve whenthe brake operation member is strongly operated.

According to a second feature of the present invention, in addition tothe first feature, the first valve means and the second valve means arearranged side by side along the axis of the control piston.

With the second feature of the present invention, the pressureincreasing valve including the first and second valve means can be madecompact.

According to a third feature of the present invention, in addition tothe first or second feature, the second valve means starts openingbefore a rate of flow from the first valve means reaches maximum.

With the third feature of the present invention, the first and secondvalve means continuously smoothly open according to the increase in thebrake operation input, thereby preventing a feeling of stepped stroke toprovide a good operation feeling.

A brake pedal 11 in an embodiment corresponds to a brake operationmember of the present invention.

The above-mentioned object, other objects, characteristics, andadvantages of the present invention will become apparent from apreferred embodiment, which will be described in detail below byreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a brake fluid pressure system and shows the entireconfiguration of a vehicle braking device.

FIG. 2 is an enlarged vertical sectional view of a master cylinder.

FIG. 3 is a vertical sectional view of a fluid pressure booster and astroke simulator.

FIG. 4 is an enlarged vertical sectional view of a pressure increasingvalve and therearound that is part of the fluid pressure booster in aclosed state.

FIG. 5 is an enlarged vertical sectional view of a pressure reducingvalve and therearound that is part of the fluid pressure booster in anopen state.

FIG. 6 is an enlarged vertical sectional view of a control piston and astroke simulator.

FIG. 7 is a sectional view corresponding to FIG. 4 at the time ofopening of a first valve means.

FIG. 8 is a sectional view corresponding to FIG. 4 at the time ofopening of a second valve means.

FIG. 9 is an enlarged view of a part 9 in FIG. 5.

FIG. 10 shows changes in flow rate of a working fluid caused by openingof the pressure increasing valve.

FIG. 11 shows an action characteristic of the stroke simulator.

DESCRIPTION OF THE PREFERRED EMBODIMENT

First in FIG. 1, a four wheel vehicle braking device includes a tandemtype master cylinder M, a fluid pressure booster 13 that regulates fluidpressure in a fluid pressure generation source 12 according to a brakeoperation force input from a brake pedal 11, which is a brake operationmember, to act on the master cylinder M, and a stroke simulator 14mounted between the brake pedal 11 and the fluid pressure booster 13.

A casing 15 common to the master cylinder M and the fluid pressurebooster 13 includes: a bottomed cylindrical cylinder body 16 with aclosed front end; and a body 17 having a cylindrical shape and an inwardflange 17 a in a rear end thereof and coaxially connected to a rearportion of the cylinder body 16. A rear end of the cylinder body 16 isfluid-tightly fitted to a front portion of the body 17. A separator 18,a first sleeve 19, and a second sleeve 20 fluid-tightly fitted to thebody 17 are held between the rear end of the cylinder body 16 and thebody 17 with the first sleeve 19 being held between the separator 18 andthe second sleeve 20.

Also with reference to FIG. 2, the cylinder body 16 has a first cylinderhole 21 with a closed front end, the master cylinder M includes: a rearmaster piston 23 having a rear surface facing a booster fluid pressureworking chamber 22 and urged backward by a spring; and a front masterpiston 24 urged backward by a spring and placed forward of the rearmaster piston 23, the rear master piston 23 and the front master piston24 being slidably fitted in the first cylinder hole 21. A rear outputfluid pressure chamber 25 is formed between the rear master piston 23and the front master piston 24, and a front output fluid pressurechamber 26 is formed between the closed front end of the cylinder body16 and the front master piston 24.

The cylinder body 16 has a rear output port 27 communicating with therear output fluid pressure chamber 25 and a front output port 28communicating with the front output fluid pressure chamber 26. A rearreturn spring 29 that urges the rear master piston 23 backward isprovided in a compressed manner between the rear master piston 23 andthe front master piston 24 in the rear output fluid pressure chamber 25.A front return spring 30 that urges the front master piston 24 backwardis provided in a compressed manner between the closed front end of thecylinder body 16 and the front master piston 24 in the front outputfluid pressure chamber 26.

A reservoir 31 is annexed to the master cylinder M, and in the reservoir31, first, second and third reservoir chambers 31 a, 31 b, and 31 c areformed in a partitioned manner. A rear connection cylindrical portioncommunicating with the second reservoir chamber 31 b and a frontconnection cylindrical portion 33 communicating with the first reservoirchamber 31 a are provided integrally with cylinder body 16 so as toprotrude upward in positions spaced apart axially of the cylinder body16.

The rear master piston 23 includes front and rear piston portions 23 aand 23 b integrally connected via a small diameter connecting portion 23c. A cup seal 34 that allows a working fluid to flow into the rearoutput fluid pressure chamber 25 and comes into slide contact with aninner surface of the first cylinder hole 21 is mounted to the frontpiston portion 23 a. A cup seal 35 that comes into slide contact withthe inner surface of the first cylinder hole 21 is mounted to the rearpiston portion 23 b.

A rear supply fluid chamber 36 having a ring shape is formed between anouter periphery of the rear master piston 23 and the inner surface ofthe first cylinder hole 21 and between the front and rear pistonportions 23 a and 23 b, and a supply port 37 normally communicating withthe rear supply fluid chamber 36 and opening into the rear connectioncylindrical portion 32 is bored in the cylinder body 16, so that a brakefluid supplied from the second reservoir chamber 31 b of the reservoir31 is fed to the rear supply fluid chamber 36.

A center valve 38 is mounted to the rear master piston 23 that providescommunication between the rear output fluid pressure chamber 25 and therear supply fluid chamber 36 when the rear master piston 23 returns to aretraction limit position.

The center valve 38 includes a valve casing 39 coaxially mounted to afront end of the rear master piston 23, an axial passage 40 thatcommunicates with the rear supply fluid chamber 36, is coaxially boredin the front piston portion 23 a of the rear master piston 23, and opensinto the front end of the front piston portion 23 a in the valve casing39, a valve body 41 that can close a front end opening of the axialpassage 40 and is housed in the valve casing 39 movably forward andbackward, a valve spring 42 that exerts a spring force for urging thevalve body 41 backward, that is, in a closing direction of the axialpassage 40 and is housed in the valve casing 39, and a stopper pin 43that holds the valve body 41 in an advanced position against an urgingforce of the valve spring 42 when the rear master piston 23 is at theretraction limit, and allows retraction, that is, closing of the valvebody 41 by the valve spring 42 at the time of advance of the rear masterpiston 23.

A long through hole 44 axially of the small diameter connecting portion23 c is provided in the small diameter connecting portion 23 c of therear master piston 23 along one diameter line of the small diameterconnecting portion 23 c, and opposite ends of the through hole 44communicate with the rear supply fluid chamber 36. The stopper pin 43 issecured to the cylinder body 16 and passes through the through hole 44,and a rear end of a valve stem 41 a connected to the valve body 41 andinserted into the axial passage 40 abuts against the stopper pin 43.

With such a center valve 38, when the rear master piston 23 is at theretraction limit, the valve stem 41 a is pressed by the stopper pin 43,and thus the valve body 41 is brought to a position for opening theaxial passage 40, so that the axial passage 40 opens to providecommunication between the rear output fluid pressure chamber 25 and thethrough hole 44, thereby supplying a supply fluid from the rear supplyfluid chamber 36 to the rear output fluid pressure chamber 25. When therear master piston 23 advances from the retraction limit, the stopperpin 43 is moved relative to the rear master piston 23 so as to be placedbackward of the through hole 44, and thus the valve body 41 is moved toa position for closing the axial passage 40 by a spring force of thevalve body 42 to block the communication between the rear supply fluidchamber 36 and the rear output fluid pressure chamber 25.

The front master piston 24 includes front and rear piston portions 24 aand 24 b integrally connected via a small diameter connecting portion 24c. A cup seal 45 that allows the working fluid to flow into the frontoutput fluid pressure chamber 26 and comes into slide contact with theinner surface of the first cylinder hole 21 is mounted to the frontpiston portion 24 a. A cup seal 46 that comes into slide contact with aninner surface of the first cylinder hole 21 is mounted to the rearpiston portion 24 b.

A front supply fluid chamber 47 having a ring shape is formed between anouter periphery of the front master piston 24 and the inner surface ofthe first cylinder hole 21 and between the front and rear pistonportions 24 a and 24 b, and a supply port 48 normally communicating withthe front supply fluid chamber 47 and opening into the front connectioncylindrical portion 33 is bored in the cylinder body 16, so that a brakefluid supplied from the first reservoir chamber 31 a of the reservoir 31is fed to the front supply fluid chamber 47.

A center valve 49 is mounted to the front master piston 24 that providescommunication between the front output fluid pressure chamber 26 and thefront supply fluid chamber 47 when the front master piston 24 returns toa retraction limit position.

The center valve 49 includes: a valve casing 50 coaxially mounted to afront end of the front master piston 24; an axial passage 51 thatcommunicates with the front supply fluid chamber 47, is coaxially boredin the front piston portion 24 a of the front master piston 24, andopens into the front end of the front piston portion 24 a in the valvecasing 50; a valve body 52 that can close a front end opening of theaxial passage 51 and is housed in the valve casing 50 movably forwardand backward; a valve spring 53 that exerts a spring force for urgingthe valve body 52 backward, that is, in a closing direction of the axialpassage 51 and is housed in the valve casing 50; and a stopper pin 54that holds the valve body 52 in an advanced position against the urgingforce of the valve spring 53 when the front master piston 24 is at theretraction limit, and allows retraction, that is, closing of the valvebody 52 by the valve spring 53 at the time of advance of the frontmaster piston 24.

A long through hole 55 axially of the small diameter connecting portion24 c is provided in the small diameter connecting portion 24 c of thefront master piston 24 along one diameter line of the small diameterconnecting portion 24 c, and opposite ends of the through hole 55communicate with the front supply fluid chamber 47. The stopper pin 54is secured to the cylinder body 16 and passes through the through hole55, and a rear end of a valve stem 52 a connected to the valve body 52and inserted into the axial passage 51 abuts against the stopper pin 54.

With such a center valve 49, when the front master piston 24 is at theretraction limit, the valve stem 52 a is pressed by the stopper pin 54,and the valve body 52 is brought to a position for opening the axialpassage 51, so that the axial passage 51 opens to provide communicationbetween the front output fluid pressure chamber 26 and the through hole55, thereby supplying a supply fluid from the front supply fluid chamber47 to the front output fluid pressure chamber 26. When the front masterpiston 24 advances from the retraction limit, the stopper pin 54 ismoved relative to the front master piston 24 so as to be placed backwardof the through hole 55, and thus the valve body 52 is moved to aposition for closing the axial passage 51 by a spring force of the valvebody 53 to block the communication between the front supply fluidchamber 47 and the front output fluid pressure chamber 26.

Specifically, the master cylinder M is of a center valve type in whichthe center valves 38 and 49 are mounted to the rear master piston 23 andthe front master piston 24, and open to supply the brake fluid from thereservoir 31 to the rear and front output fluid pressure chambers 25 and26 at the time of retraction of the rear master piston 23 and the frontmaster piston 24.

A maximum space restricting means 56 that restricts a maximum spacebetween the rear and front master pistons 23 and 24 are provided betweenthe master pistons 23 and 24. The maximum space restricting means 56includes a retainer 57 that abuts against a rear surface of the rearpiston portion 24 b in the front master piston 24, a rod 58 that isconnected to a middle of a front end of the valve casing 39 in thecenter valve 38 mounted to the rear master piston 23 and extendedforward, and that has a front portion movably inserted into the middleof the retainer 57, and an engaging member 59 screwed into a front endof the rod 58 so as to engage the retainer 57 from the front. Further,the rear return spring 29 is provided in a compressed manner between thevalve casing 39 and the retainer 57, and the retainer 57 issubstantially secured to the front master piston 23.

With such a maximum space restricting means 56, the engaging member 59engages the middle of the retainer 57 from the front to restrict themaximum space between the rear and front master pistons 23 and 24.

Returning to FIG. 1, the rear output port 27 in the master cylinder M isconnected to a right front wheel brake B1 and a left rear wheel brake B2via a fluid pressure modulator 60, and the front output port 28 isconnected to a left front wheel brake B3 and a right rear wheel brake B4via the fluid pressure modulator 60. The fluid pressure modulator 60 isa known one that can freely control brake fluid pressure output from therear and front output ports 27 and 28 to perform anti-lock brake controlat the time of brake operation and perform automatic brake control suchas traction control in a non-braking operation state.

In FIG. 3, the fluid pressure booster 13 includes a cylindrical backuppiston 64 that has a front end facing the booster fluid pressure workingchamber 22 and is slidably housed in the body 17 of the casing 15,pressure regulating valve means 65 constituted by a pressure increasingvalve 106 and a pressure reducing valve 107 and built in the backuppiston 64, a control piston 66 that causes the pressure regulating valvemeans 65 to regulate pressure and establishes a balance between reactionbased on fluid pressure in a booster fluid pressure generation chamber121 connected to the booster fluid pressure working chamber 22 and thebrake operation input that is input from the brake pedal 11, a firstreaction piston 67 that is mounted between the pressure regulating valvemeans 65 and the control piston 66 so as to apply the reaction based onthe fluid pressure in the booster fluid pressure generation chamber 121to the control piston 66, and a second reaction piston 68 mountedbetween the backup piston 64 and the first reaction piston 67 so as toapply reaction caused by output fluid pressure from the fluid pressuregeneration source 12 and reaction by a reaction spring 112 to thecontrol piston 66 in addition to the reaction from the first reactionpiston 67 when the brake operation input by the brake pedal 11 isincreased.

The body 17 that constitutes part of the casing 15 and is coaxiallyconnected to the rear portion of the cylinder body 16 includes: a largediameter hole 69 that fluid-tightly fits the rear end of the cylinderbody 16, the separator 18, the first sleeve 19, and the second sleeve 20from the front end; and a medium diameter hole 71 that forms an annularstep 70 with a rear end of the large diameter hole 69, is coaxiallyconnected to the rear end of the large diameter hole 69, and has asmaller diameter than the large diameter hole 69. The inward flange 17 aprovided in the rear end of the body 17 so as to define a rear end ofthe medium diameter hole 71 forms a small diameter hole 72 having asmaller diameter than the medium diameter hole 71.

The separator 18, the first sleeve 19, and the second sleeve 20 arefluid-tightly fitted in the large diameter hole 69 so as to be heldbetween the rear end of the cylinder body 16 of the master cylinder Mand the step 70 with a leaf spring 73 being mounted between theseparator 18 and the first sleeve 19. Thus, the separator 18, the firstsleeve 19, and the second sleeve 20 are reliably secured to the frontportion of the body 17 while absorbing dimensional tolerance to adistance between the rear end of the cylinder body 16 and the step 70 bya spring force exerted by the leaf spring 73.

The separator 18 has a short cylindrical shape and an inner peripherythat forms a second cylinder hole 74 having a slightly smaller diameterthan the first cylinder hole 21 of the cylinder body 16 of the mastercylinder M. The first sleeve 19 has a cylindrical shape that forms athird cylinder hole 75 having the same diameter as the first cylinderhole 21. Further, the second sleeve 20 has a stepped cylindrical shapeand integrally includes a large diameter potion 20 a fitted in the largediameter hole 69 of the body 17, and a small diameter portion 20 b thatforms a fourth cylinder hole 76 having a slightly smaller diameter thanthe second cylinder hole 74 and extends backward from the large diameterpotion 20 a. The rear end of the small diameter potion 20 a abutsagainst the step 70. Thus, the separator 18, the first sleeve 19, andthe second sleeve 20 fluid-tightly fitted and secured in the body 17form, sequentially from the front, the second to fourth cylinder holes74, 75 and 76 coaxial with the first cylinder hole 21.

The backup piston 64 integrally includes a front small diameter portion64 a slidably fitted in the second cylinder hole 74, a rear smalldiameter portion 64 b having a slightly smaller outer diameter than thefront small diameter portion 64 a and slidably fitted in the fourthcylinder hole 76, and a middle large diameter potion 64 c that connectsthe front small diameter portion 64 a and the rear small diameterportion 64 b and that is inserted into the third cylinder hole 75 with agap. The backup piston 64 has a stepped cylindrical shape with themiddle large diameter potion 64 c having a diameter larger than those ofthe front small diameter portion 64 a and the rear small diameterportion 64 b.

The body 17 has a connection port 77 opening into an inner surface ofthe large diameter hole 69 in a position corresponding to a portionbetween the cylinder body 16 of the master cylinder M and the separator18, an input port 78 opening into the inner surface of the largediameter hole 69 in a position corresponding to a portion between theseparator 18 and the first sleeve 19, an output port 79 opening into theinner surface of the large diameter hole 69 in an axially middle portionof the first sleeve 19, and a release port 80 opening into a front innersurface of the medium diameter hole 71, which are provided sequentiallyfrom the front with spaces therebetween.

As shown in FIG. 1, the fluid pressure generation source 12 is connectedto the input port 78. The fluid pressure generation source 12 includes:a pump 81 for drawing up the working fluid from the third reservoirchamber 31 c of the reservoir 31; an accumulator 82 connected to adischarge side of the pump 81; and a fluid pressure sensor 83 fordetecting fluid pressure of the accumulator 82 to control actuation ofthe pump 81. A constant high fluid pressure is fed from the fluidpressure generation source 12 to the input port 78. The release port 80is connected to the second reservoir chamber 31 b of the reservoir 31.

The inner surface of the large diameter hole 69 in the body 17 has anannular recess 86 that opens an inner end of the connection port 77, anannular recess 87 that opens an inner end of the input port 78, and anannular recess 88 that opens an inner end of the output port 79. O rings89, 90, 91, and 92 that are annular seal members that seal the annularrecesses 86, 87, and 88 from opposite sides are mounted to outerperipheries of the cylinder body 16 of the master cylinder M, theseparator 18, the first sleeve 19, and the second sleeve 20.Specifically, the O rings 89 and 90 that seal the annular recess 86 fromopposite sides are mounted to the outer peripheries of the cylinder body16 and the separator 18 so as to come into repulsive contact with theinner surface of the large diameter hole 69. The O ring 91 that holdsthe annular recess 87 with the O ring 90 is mounted to the outerperiphery of the first sleeve 19 so as to come into repulsive contactwith the inner surface of the large diameter hole 69. The O ring 92 thatholds the annular recess 88 with the O ring 91 is mounted to the outerperiphery of the large diameter potion 20 a in the second sleeve 20 soas to come into repulsive contact with the inner surface of the largediameter hole 69.

When the separator 18, the first sleeve 19, and the second sleeve 20 arefitted in the large diameter hole 69, the O ring 92 mounted to the outerperiphery of the second sleeve 20 needs to pass over the annularrecesses 86 to 88, the O ring 91 mounted to the outer periphery of thefirst sleeve 19 needs to pass over the annular recesses 86 and 87, andthe O ring 90 mounted to the outer periphery of the separator 18 needsto pass over the annular recess 86. If two or more O rings among thethree O rings 90 to 92 simultaneously pass through a plurality of frontedges in a fitting direction of the annular recesses 86 to 88, fittingof the separator 18, the first sleeve 19, and the second sleeve 20 needsa large force, and an excessive force may damage the O rings 90 to 92,thereby affecting assemblability.

Thus, spaces L1 and L2 between the front edges of the annular recesses86 to 88 in the direction of fitting the separator 18, the first sleeve19, and the second sleeve 20 into the body 17 are set to values thatprevent the plurality of O rings 90 to 92 from simultaneously passingover the front edges when the separator 18, the first sleeve 19, and thesecond sleeve 20 are fitted into the body 17. In the embodiment, thespace L1 between the front edges of the annular recesses 86 and 87 isset to a smaller value than a space L3 between the O rings 90 and 91,and the space L2 between the front edges of the annular recesses 87 and88 is set to a smaller value than a space L4 between the O rings 91 and92.

Also with reference to FIG. 4, the front small diameter portion 64 a inthe backup piston 64 is fluid-tightly and slidably fitted in the secondcylinder hole 74 of the separator 18, the middle large diameter potion64 c of the backup piston 64 is fluid-tightly and slidably fitted in thethird cylinder hole 75 of the first sleeve 19, an annular passage 93 isformed between the outer periphery of the front small diameter portion64 a and the inner periphery of the first sleeve 19, a channel 94communicating with the annular passage 93 is formed between theseparator 18 and the first sleeve 19, so that the channel 94 providescommunication between the annular recess 87 communicating with the inputport 78 and the annular passage 93.

Further, front and rear sides of the annular passage 93 are sealed by anO ring 95 that is an annular seal member mounted between the separator18 and the backup piston 64, and an O ring 96 that is an annular sealmember mounted between the first sleeve 19 and the backup piston 64. TheO ring 95 is mounted to the inner surface of the separator 18, that is,the inner surface of the second cylinder hole 74 so as to come intorepulsive slide contact with the outer periphery of the front smalldiameter portion 64 a in the backup piston 64. The O ring 96 is mountedto the outer surface of the middle large diameter potion 64 c in thebackup piston 64 so as to come into repulsive contact with the innersurface of the third cylinder hole 75, that is, the inner periphery ofthe first sleeve 19.

Also with reference to FIG. 5, an O ring 97 that comes into repulsivecontact with the outer periphery of the rear small diameter portion 64 bin the backup piston 64 is mounted to the inner periphery of the smalldiameter portion 20 b in the second sleeve 20, that is, the innersurface of the fourth cylinder hole 76. On the other hand, a channel 98having an outer end communicating with the annular recess 88 provided inthe inner surface of the body 17 so as to communicate with the outputport 79 is provided in the first and second sleeves 19 and 20. Anannular recess 99 communicating with the channel 98 is formed in theinner periphery of the first sleeve 19 and the inner periphery of thesmall diameter portion 20 b in the second sleeve 20 between the firstand second sleeves 19 and 20. Front and rear sides of the annular recess99 are sealed by the O rings 96 and 97.

On the other hand, as shown in FIG. 3, a ring-shaped stopper 100 abutsagainst the inward flange 17 a in the body 17, a coil spring 103surrounding a rear half of the backup piston 64 is provided in acompressed manner between a retainer 102 and the second sleeve 20, theretainer 102 having an inner periphery that abuts against and engages,from the front, a snap ring 101 mounted to the outer periphery of therear end of the rear small diameter portion 64 b in the backup piston64. The backup piston 64 is urged backward by a spring force of thespring 103. Thus, the position where the snap ring 101 abuts against thestopper 100 that abuts against the inward flange 17 a in the body 17 isa retraction limit of the backup piston 64, the front end of the backuppiston 64 at the retraction limit faces the booster fluid pressureworking chamber 22, and abuts against the entire outer peripheral edgeof the rear surface of the rear master piston 23 in a non-operationstate, and in this state, the rear master piston 23 is at the retractionlimit.

As clearly shown in FIG. 4, a groove 138 radially extending so as toform a passage 137 with the front end of the body 17 that abuts againstthe rear end of the cylinder body 16 is provided in an upper portion ofthe rear end of the cylinder body 16 of the master cylinder M, and thepassage 137 provides communication between the annular recess 86communicating with the connection port 77 and the booster fluid pressureworking chamber 22. A groove 140 is provided in the rear end of the rearmaster piston 23 so as to form a passage 139 for leading booster fluidpressure to between the rear surface of the master piston 23 and thefront end of the backup piston 64, with the front end of the backuppiston 64 that abuts against the rear end of the master piston 23. Thegroove 140 is formed to extend along one diameter line of the rearmaster piston 23 in parallel with an axis of the through hole 44provided in the rear master piston 23, that is, an axis of the stopperpin 43.

Thus, the connection port 77 communicates with the booster fluidpressure working chamber 22 via the annular recess 86 and the passage137, and the passage 139 causes the fluid pressure in the booster fluidpressure working chamber 22 to act on a portion between the rear masterpiston 23 and the backup piston 64 in a state in which the backup piston64 abuts against the rear master piston 23.

Between the second sleeve 20 and the inward flange 17 a in the body 17,a spring chamber 104 is formed that surrounds the backup piston 64 so asto house the spring 103, and the spring chamber 104 communicates withthe release port 80. The O ring 97 seals a portion between the springchamber 104 and the annular recess 99 communicating with the output port79.

An inward flange 64 d protruding radially inward is integrally providedin the inner surface of the axially middle portion of the backup piston64, and an insertion hole 108 coaxial with the backup piston 64 isformed in the inner periphery of the inward flange 64 d. The steppedcylindrical second reaction piston 68 is slidably fitted to the backuppiston 64 forward of the inward flange 64 d, and the first reactionpiston 67 is coaxially and relatively slidably fitted to the reactionpiston 68.

An end wall member 109 having a front surface facing the booster fluidpressure working chamber 22 is fluid-tightly fitted to the front end ofthe backup piston 64, and a snap ring 110 that abuts against and engagesan outer peripheral edge of the end wall member 109 from the front ismounted to the inner periphery of the front end of the backup piston 64.Further, a filter 111, in which a mesh member 129 is provided in aninner surface of a filter frame 127 having a plurality of openings 128in a circumferential direction and a bottomed cylindrical shape, ismounted to the front end of the second reaction piston 68, and thesecond reaction piston 68 is urged to abut against the inward flange 64d from the front by the spring force of the reaction spring 112 providedin a compressed manner between the filter 111 and the end wall member109.

An input chamber 113 is formed in the backup piston 64 between thesecond reaction piston 68 and the filter 111 and the end wall member109, and the input chamber 113 communicates with the annular passage 93via a communication hole 114 provided in the backup piston 64.Specifically, the high pressure working fluid from the fluid pressuregeneration source 12 is introduced into the input chamber 113, and an Oring 115 is mounted to an outer periphery of the end wall member 109 toseal between the input chamber 113 and the booster fluid pressureworking chamber 22 and come into repulsive contact with the innerperiphery of the backup piston 64.

An annular step 68 a facing forward is provided in the inner surface ofthe middle of the second reaction piston 68, a stepped cylindrical valveseat member 117 having, in an outer periphery thereof, an O ring 116that comes into repulsive contact with the inner periphery of the secondreaction piston 68 is fitted to the front portion of the second reactionpiston 68 so as to abut against the step 68 a, and a leaf spring 119 isprovided between the valve seat member 117 and a snap ring 118 mountedto the inner periphery of the second reaction piston 68 forward of thevalve seat member 117. Thus, the valve seat member 117 is fluid-tightlyfitted and secured to the front portion of the second reaction piston68, and supported by the backup piston 64 via the second reaction piston68.

On the other hand, the first reaction piston 67 has, in the outerperiphery thereof, an annular seal member 120 that comes into repulsivecontact with the inner periphery of the rear portion of the secondreaction piston 68, and is slidably fitted to the front portion of thesecond reaction piston 68. The booster fluid pressure generation chamber121 is formed in the second reaction piston 68 so as to face the rearsurface of the valve seat member 117 and the front end of the firstreaction piston 67. An annular chamber 122 is formed between the outerperiphery of the second reaction piston 68 and the inner periphery ofthe backup piston 64. The booster fluid pressure generation chamber 121communicates with the annular chamber 122 via a communication hole 123provided in the second reaction piston 68. Further, a communication hole124 that provides communication between the annular chamber 122 and theannular recess 99 is provided in the middle large diameter potion 64 cin the backup piston 64. The booster fluid pressure generation chamber121 communicates with the output port 79 via the communication hole 123,the annular chamber 122, the communication hole 124, the annular recess99, and the channel 98. Further, O rings 125 and 126 that hold theannular chamber 122 from the front and back is mounted to the outerperiphery of the second reaction piston 68 so as to come into repulsivecontact with the inner periphery of the backup piston 64.

In FIG. 6, the control piston 66 has a bottomed cylindrical shape withan end wall 66 a at a front end thereof, and is slidably fitted in thesmall diameter hole 72 formed by the inward flange 17 a in the rear endof the body 17 and coaxially inserted into the rear small diameterportion 64 b in the backup piston 64. Further, an annular seal member130 that comes into repulsive contact with the outer periphery of thecontrol piston 66 is mounted to the inner periphery of the inward flange17 a, that is, the inner surface of the small diameter hole 72. Arestriction protrusion 131 that abuts against and engages the innerperipheral edge of the inward flange 17 a from the front to restrict theretraction limit of the control piston 66 is integrally provided in theouter surface of the control piston 66 in a protruding manner over theentire periphery.

A release chamber 132 is formed in the rear of the inward flange 64 dand between the backup piston 64 and the control piston 66. The releasechamber 132 communicates with the spring chamber 104 via a communicationhole 133 provided in the stopper 100. Specifically, the release chamber132 communicates with the third reservoir chamber 31 c of the reservoir31 via the communication hole 133, the spring chamber 104, and therelease port 80.

The first reaction piston 67 coaxially and integrally includes anextended cylindrical portion 67 a extending backward through theinsertion hole 108. A rear end of the extended cylindrical portion 67 anormally abuts against the end wall 66 a of the front end of the controlpiston 66. A spring 134 is housed in the booster fluid pressuregeneration chamber 121 so as to exert a spring force for urging the rearend of the first reaction piston 67, that is, the rear end of theextended cylindrical portion 67 a to come into contact with the end wall66 a of the control piston 66. The spring force of the spring 134 is setto an extremely small value.

The second reaction piston 68 coaxially and integrally includes anextended cylindrical portion 68 b that coaxially surrounds the extendedcylindrical portion 67 a of the first reaction piston 67 and is insertedinto the insertion hole 108. In a state in which the second reactionpiston 68 abuts against the inward flange 64 d of the backup piston 64at the retraction limit position, a rear end of the extended cylindricalportion 68 b of the second reaction piston 68 is placed backward of aseat stopper 135 that abuts against the inward flange 64 d of the backuppiston 64 and that is secured to the backup piston 64, and forward ofthe rear end of the extended cylindrical portion 67 a of the firstreaction piston 67.

Thus, in an advancing operation of the control piston 66 relative to thebackup piston 64, the first reaction piston 67 advances together withthe control piston 66, and the rear end of the second reaction piston 68abuts against the end wall 66 a of the front end of the control piston66 when the brake operation input by the brake pedal 11 is increased andthe amount of advancing movement of the control piston 66 becomes largerthan a predetermined value.

Returning to FIG. 4, the pressure increasing valve 106 includes firstand second valve means 141 and 142 arranged side by side along the axisof the control piston 66 so as to sequentially open according to theincrease in the brake operation input from the brake pedal 11. A sealdiameter of the second valve means 142 is larger than a seal diameter ofthe first valve means 141, and the second valve means 142 is designed tostart opening before a rate of flow from the opened first valve means141 reaches maximum.

The first valve means 141 includes: a cylindrical slide member 144having a first valve seat 143 in a front end thereof; a retainer 146that forms valve chamber 145 therein that communicates with the inputchamber 113 communicating with the fluid pressure generation source 12;a valve body 147 that can be seated on the first valve seat 143 facingthe valve chamber 145 and is slidably fitted to the retainer 146; afirst valve spring 148 that urges the valve body 147 to be seated on thefirst valve seat and is provided between the retainer 146 and the valvebody 147; and a pressing rod 149 that can abut against the valve body147, cooperates with and is connected to the control piston 66, and isinserted into the slide member 144 relatively movably in the axialdirection.

The second valve means 142 includes: a valve portion 150 provided in theslide member 144 that is the common component shared with the firstvalve means 141; the stepped cylindrical valve seat member 117 thatslidably fits the slide member 144 and has a front end on which a secondvalve seat 151 is provided; the retainer 146 that is also the componentof the first valve means 141; a second valve spring 152 that urges thevalve portion 150 to be seated on the second valve seat 151 and isprovided between the retainer 146 and the slide member 144; and thepressing rod 149 that is also the component of the first valve means141.

The slide member 144 and the valve seat member 117 constitute insertedmeans 156 that is inserted into and supported by the second reactionpiston 68 with the slide member 144 being slidably fitted to the valveseat member 117. The second reaction piston 68 is slidably fitted to thebackup piston 64, and thus the inserted means 156 is inserted into andsupported by the backup piston 64.

The retainer 146 is mounted to the outer periphery of the front end ofthe valve seat member 117 that constitutes part of the inserted means156 by press fitting. The valve chamber 145 is formed in the retainer146 to face the first valve seat 143 in the front end of the slidemember 144 and the second valve seat 151 in the front end of the valveseat member 117. A guide cylindrical portion 146 b is integrallyprovided in the front portion of the retainer 146. The retainer 146 hasa bottomed cylindrical shape and has, in a front end thereof, an endwall 146 a having an open hole 153 communicating with the input chamber113 in a central part thereof. The valve body 147 of the first valvemeans 141 is formed by a sphere 155 that can be seated on the firstvalve seat 143 being secured to a rear portion of a slide member 154slidably fitted to the guide cylindrical portion 146 b. Specifically,the valve body 147 is slidably fitted to the retainer 146, and the firstvalve spring 148 is provided in a compressed manner between the end wall146 a and the slide member 154.

The slide member 144 coaxially has a first valve hole 157 having a frontend opening into a central part of the first valve seat 143, and a slidehole 158 having a diameter larger than the first valve hole 157, a frontend communicating with the first valve hole 157, and an open rear end.On the other hand, the valve seat member 117 coaxially has a secondvalve hole 159 having a front end opening into a central part of thesecond valve seat 151, and a slide hole 160 having the same diameter asthe second valve hole 159, a front end communicating with the secondvalve hole 159, and an open rear end. The slide member 144 coaxially andmovably passes through the second valve hole 159, and is slidably fittedin the slide hole 160.

The pressing rod 149 is slidably fitted in the slide hole 158 of theslide member 144 with the front end thereof being placed in the firstvalve hole 157. A pressing flange 149 a that can abut against the rearend of the slide member 144 to press and move the slide member 144forward is integrally provided in the pressing rod 149 in the valve seatmember 117. A restriction flange 117 a that abuts against the pressingflange 149 a from behind to restrict a retraction limit of the pressingrod 149 is integrally provided in the valve seat member 117 so as toprotrude radially inward from an inner surface of a rear portion of theslide hole 160.

A slide portion 149 b that comes into slide contact with an innersurface of the slide hole 158 is provided in the pressing rod 149forward of the pressing flange 149 a. The pressing rod 149 has a smalldiameter forward of the slide portion 149 b so as to form an annularchamber 163 with the inner surface of the slide member 144.

As shown in FIG. 7, when the valve body 147 is pressed by the front endof the pressing rod 149 to separate the valve body 147 from the firstvalve seat 143, the valve chamber 145 communicates with the annularchamber 163. Further, in a state in which the pressing flange 149 aabuts against the restricting step 117 a, a distance between the frontend of the pressing rod 149 and the valve body 147 is smaller than adistance between the rear end of the slide member 144 and the pressingflange 149 a. At the time of advance of the pressing rod 149, thepressing rod 149 further advances after the valve body 147 is separatedfrom the first valve seat 143, and thus the pressing flange 149 afurther presses the slide member 144 forward.

The valve portion 150 of the second valve means 142 is provided in theslide member 144 in the rear of the first valve seat 143, has a sealdiameter larger than a seal diameter when the valve body 147 is seatedon the first valve seat 143, and can be seated on the second valve seat151. After the first valve means 141 opens, as shown in FIG. 8, thepressing rod 149 further advances to press the slide member 144 forward,and thus the valve portion 150 is separated from the second valve seat151 to open the second valve means 142.

A plurality of flow grooves 161 having rear ends opening into the rearend of the valve seat member 117 are provided in the inner surface ofthe slide hole 160 in the valve seat member 117. A plurality ofcommunication holes 164 that provides communication between the annularchamber 163 and the flow grooves 161 are provided in the slide member144.

The slide hole 160 and the plurality of flow grooves 161 in the valveseat member 117 form a flow passage 162, and at the time of opening ofthe first valve means 141, a working fluid flowing from the valvechamber 145 into the annular chamber 163 flows through the flow passage162 via the communication holes 164 toward the booster fluid pressuregeneration chamber 121, and at the time of opening of the second valvemeans 142, the working fluid in the valve chamber 145 flows through theflow passage 162 toward the booster fluid pressure generation chamber121.

A plurality of communication holes 165 are provided in a side wall ofthe retainer 146.so as to provide communication between the inputchamber 113 communicating with the fluid pressure generation source 12and the valve chamber 145. The communication holes 165 are provided inthe side wall of the retainer 146 so as to be placed on a side oppositefrom the valve body 147, that is, a rear side relative to a seatingposition of the valve body 147 on the first valve seat 143 in the firstvalve means 141.

A rear portion of the pressing rod 149 protrudes into the booster fluidpressure generation chamber 121, and the pressing rod 149 is slidablyfitted to a middle of a disk-shaped rectifying member 168 in the boosterfluid pressure generation chamber 121. The rectifying member 168 abutsagainst a surface of the valve seat member 117 facing the booster fluidpressure generation chamber 121 to close an open end of the flow passage162 opening into the booster fluid pressure generation chamber 121, andan axial movement thereof is guided by the pressing rod 149 only.Further, a surface of the rectifying member 168 facing the flow passage162 is a flat surface 168 a.

With reference to FIG. 5, a spring receiving member 169 is pressed intoand secured to the pressing rod 149 backward of the rectifying member168, and a spring 170 is provided in a compressed manner between therectifying member 168 and the spring receiving member 169. On the otherhand, the front end of the first reaction piston 67 also protrudes intothe booster fluid pressure generation chamber 121 coaxially with thepressing rod 149, and the spring 134 is provided in a compressed mannerbetween a retainer 171 that fits and abuts against the front portion ofthe first reaction piston 67 and the rectifying member 168. Thus, therectifying member 168 is urged toward the valve seat member 117 byspring forces of the springs 134 and 170. The spring forces of thesprings 134 and 170 are set so that the rectifying member 168 can bespaced from the valve seat member 117 according to the fluid pressurefrom the fluid pressure generation source 12 acting on the flow passage162 by the opening of the first valve means 141.

The retainer 171 fitted to the front portion of the first reactionpiston 67 forms a valve chamber 172 with the first reaction piston 67,and a plurality of communication holes 173 are provided in the retainer171 so as to provide communication between the booster fluid pressuregeneration chamber 121 and the valve chamber 172. A guide cylindricalportion 174 is provided in a middle of the retainer 171, and the rearend of the pressing rod 149 is slidably fitted into the guidecylindrical portion 174. A valve seat 175 is provided in the front endof the first reaction piston 67 to face the valve chamber 172, and avalve portion 176 having a hemispherical shape is provided in the rearend of the pressing rod 149 so as to be seated on the valve seat 175.

The pressure reducing valve 107 includes the valve seat 175, and thevalve portion 176 that can be seated on the valve seat 175. The firstreaction piston 67 axially has a valve hole 177 opening into a centralpart of the valve seat 175, and a release passage 178 having a largerdiameter than the valve hole 177 and a front end communicating with thevalve hole 177, and extending to the rear end of the first reactionpiston 67. The end wall 66 a of the front end of the control piston 66normally abuts against the rear end of the first reaction piston 67 tosubstantially close the rear end of the release passage 178.

A plurality of communication holes 179 having inner ends communicatingwith the release passage 178 are provided in the middle of the firstreaction piston 67, and at the time of opening of the pressure reducingvalve 107, a working fluid from the release passage 178 flows into therelease chamber 132 via the communication holes 179, a temporary storagechamber 180, and an orifice 181.

The temporary storage chamber 180 is formed between the first and secondreaction pistons 67 and 68, and has a ring shape surrounding the firstreaction piston 67 between an annular step 67 b provided in the outerperiphery of the first reaction piston 67 to face backward, and anannular step 68 c provided in the inner periphery of the second reactionpiston 68 to face forward so as to face the step 67 a.

The orifice 181 is formed between an outer periphery of the extendedcylindrical portion 67 a of the first reaction piston 67 and an innerperiphery of the extended cylindrical portion 68 b of the secondreaction piston 68. The orifice 181 is formed by setting an annular gapby an amount of tolerance between the outer periphery of the extendedcylindrical portion 67 a and the inner periphery of the extendedcylindrical portion 68 b.

Further, the communication holes 179 are provided in the first reactionpiston 67 so as to be placed in a position corresponding to thetemporary storage chamber 180 at least when the pressure reducing valve107 starts opening from a closing state.

In such a fluid pressure booster 13, the brake operation input from thebrake pedal 11 is input to the control piston 66 via the strokesimulator 14, and a forward pressing force acts on the first reactionpiston 67 from the control piston 66. In a state in which the amount ofadvancing movement of the control piston 66 relative to the backuppiston 64 is less than a predetermined value, only the first reactionpiston 67 abuts against the control piston 66, the valve portion 176 isseated on the valve seat 175 according to the advance of the firstreaction piston 67 to close the pressure reducing valve 107 and blockthe communication between the booster fluid pressure generation chamber121 and the release chamber 132, and the control piston 66, the firstreaction piston 67, and the pressing rod 149 further advance. Accordingto the advance of the pressing rod 149, in the pressure increasing valve106, the valve body 147 is first separated from the first valve seat 143at the front end of the slide member 144 to open the first valve means141, then the pressing rod 149 further advances and presses the slidemember 144, and the valve portion 150 is separated from the second valveseat 151 to open the second valve means 142.

In the closing state of the pressure reducing valve 107, the fluidpressure in the booster fluid pressure generation chamber 121 acts onthe front end of the first reaction piston 67, the first reaction piston67 and the control piston 66 are retracted so that the brake operationinput from the brake pedal 11 and the fluid pressure based on the fluidpressure in the booster fluid pressure generation chamber 121 arebalanced to open the pressure reducing valve 107 and close the pressureincreasing valve 106. The opening and closing of the pressure increasingvalve 106 and the pressure reducing valve 107 are repeated, and thus theoutput fluid pressure of the fluid pressure generation source 12 isregulated to a booster fluid pressure according to the brake operationinput from the brake pedal 11, and applied to the booster fluid pressuregeneration chamber 121. When the amount of advancing movement of thecontrol piston 66 relative to the backup piston 64 reaches apredetermined value or more, the first reaction piston 67 and also thesecond reaction piston 68 abut against the control piston 66, and thefluid pressure that presses the second reaction piston 68 backward bythe fluid pressure of the input chamber 113 and the spring force of thereaction spring 112 are also added as reaction forces, therebyincreasing the reaction that acts on the control piston 66.

With reference to FIG. 1, the connection port 77 provided in the body 17so as to communicate with the booster fluid pressure working chamber 22is connected to the fluid pressure generation source 12 via a normallyclosed automatic brake pressurizing linear solenoid valve 184, andconnected to the third reservoir chamber 31 c of the reservoir 31 via anormally closed regenerative cooperative pressure reducing linearsolenoid valve 185. Specifically, the normally closed automatic brakepressurizing linear solenoid valve 184 is provided between the boosterfluid pressure working chamber 22 and the fluid pressure generationsource 12, and the normally closed regenerative cooperative pressurereducing linear solenoid valve 185 is provided between the booster fluidpressure working chamber 22 and the reservoir 31.

The output port 79 communicating with the booster fluid pressuregeneration chamber 121 is connected to the connection port 77 via anormally open automatic brake pressure reducing linear solenoid valve186 and a normally open regenerative cooperative pressurizing linearsolenoid valve 187 connected in series. A first one-way valve 188 isconnected to the automatic brake pressure reducing linear solenoid valve186 in parallel so as to allow the working fluid to flow from the outputport 79 toward the connection port 77, and a second one-way valve 189 isconnected to the regenerative cooperative pressurizing linear solenoidvalve 187 in parallel so as to allow the working fluid to flow from theconnection port 77 toward the output port 79.

Specifically, the automatic brake pressure reducing linear solenoidvalve 186 to which the first one-way valve 188 is connected in parallel,and the regenerative cooperative pressurizing linear solenoid valve 187to which the second one-way valve 189 is connected in parallel areprovided between the booster fluid pressure generation chamber 121 andthe booster fluid pressure working chamber 22.

Further, a brake operation amount detecting fluid pressure sensor 190 isconnected between the output port 79 and the automatic brake pressurereducing linear solenoid valve 186, and an automatic brake feedbackcontrolling fluid pressure sensor 191 is connected between theregenerative cooperative pressurizing linear solenoid valve 187 and theconnection port 77.

As described above, the normally closed automatic brake pressurizinglinear solenoid valve 184 is provided between the fluid pressuregeneration source 12 and the booster fluid pressure working chamber 22,and the normally open automatic brake pressure reducing linear solenoidvalve 186 and the first one-way valve 188 connected to the automaticbrake pressure reducing linear solenoid valve 186 in parallel so as toallow the brake fluid to flow from the booster fluid pressure generationchamber 121 toward the booster fluid pressure working chamber 22 areprovided between the booster fluid pressure generation chamber 121 andthe booster fluid pressure working chamber 22. Thus, even at the time ofnon-operation of the brake pedal 11, that is, the time of non-operationof the pressure regulating valve means 65, opening and closing of theautomatic brake pressurizing linear solenoid valve 184 and the automaticbrake pressure reducing linear solenoid valve 186 are controlled toregulate the fluid pressure in the booster fluid pressure workingchamber 22, thereby performing automatic brake control such that thebrake fluid pressure acts on the wheel brakes B1 to B4 in thenon-braking operation state. Further, when the brake pedal 11 isoperated with the automatic brake pressure reducing linear solenoidvalve 186 being closed to actuate the pressure regulating valve means 65at the time of automatic braking, so that fluid pressure higher than thefluid pressure in the booster fluid pressure working chamber 22 isgenerated in the booster fluid pressure generation chamber 121, thefluid pressure in the booster fluid pressure generation chamber 121 canbe caused to act on the booster fluid pressure working chamber 22 viathe first one-way valve 188, to actuate the master cylinder M in thesame way as in the case of normal brake operation.

The normally closed regenerative cooperative pressure reducing linearsolenoid valve 185 is provided between the booster fluid pressureworking chamber 22 and the reservoir 31, and the normally openregenerative cooperative pressurizing linear solenoid valve 187 and thesecond one-way valve 189 connected to the regenerative cooperativepressurizing linear solenoid valve 187 in parallel so as to allow thebrake fluid to flow from the booster fluid pressure working chamber 22toward the booster fluid pressure generation chamber 121 are providedbetween the booster fluid pressure generation chamber 121 and thebooster fluid pressure working chamber 22. Thus, at the time ofregeneration in the brake operation state, the opening and closing ofthe regenerative cooperative pressurizing linear solenoid valve 187 andthe regenerative cooperative pressure reducing linear solenoid valve 185are controlled to regulate the fluid pressure in the booster fluidpressure working chamber 22, and thus brake fluid pressure offset fromthe pressure at the time of normal braking can be output from the mastercylinder M, and when the brake pedal 11 is returned at the time ofclosing of the regenerative cooperative pressurizing linear solenoidvalve 187, the fluid pressure in the booster fluid pressure workingchamber 22 can be released toward the reservoir 31 via the secondone-way valve 189.

With reference to FIG. 6, the stroke simulator 14 forms a stroke fluidchamber 193 with the end wall 66 a of the front end of the controlpiston 66, includes: an input piston 194 as an input member fitted tothe control piston 66 fluid-tightly and slidably in the axial direction;and repulsive means 195 mounted between the input piston 194 and the endwall 66 a of the control piston 66 and housed in the stroke fluidchamber 193, and is included in the control piston 66.

The input piston 194 is slidably fitted to the rear portion of thecontrol piston 66 so that a retraction limit position is restricted by asnap ring 196 mounted to the rear end of the control piston 66, and afront end of an input rod 197 connected to the brake pedal 11 isoscillably connected to the input piston 194. Specifically, the brakeoperation force according to the operation of the brake pedal 11 isinput to the input piston 194 via the input rod 197, and the inputpiston 194 advances according to the input of the brake operation force.Further, an annular seal member 198 that comes into slide contact withthe inner periphery of the control piston 66 is mounted to the outerperiphery of the input piston 194.

The repulsive means 195 includes an elastic body 199 made of an elasticmaterial such as rubber and having a cylindrical shape, and a metal coilspring 200 having a spring load smaller than the elastic body 199,connected in series via a slide member 201 slidably housed in thecontrol piston 66. The elastic body 199 is provided between the slidemember 201 and the input piston 194, and the coil spring 200 is providedbetween the end wall 66 a of the front end of the control piston 66 andthe slide member 201.

Further, the elastic body 199 and the coil spring 200 are mounted inseries between the input piston 194 and the control piston 66 so that aspring force exerted by the coil spring 200 acts on the control piston66 in early stages of the brake operation of the brake pedal 11, and theslide member 201 abuts against the end wall 66 a of the front end of thecontrol piston 66 to start elastic deformation of the elastic body 199after the action of the spring force of the coil spring 200 on thecontrol piston 66 is finished.

The coil spring 200 has a set load lower than other spring membersconnected to the coil spring 200 in series so as to exert forward andbackward spring forces. In this embodiment, the set load is lower than aset load of the spring 134 connected to the coil spring 200 in seriesvia the first reaction piston 67 and the end wall 66 a of the controlpiston 66 and housed in the booster fluid pressure generation chamber121.

A front end of a guide shaft 202 that is coaxial with the control piston66 and passes through the elastic body 199 is pressed into a middle ofthe slide member 201, and a rear end of the guide shaft 202 is slidablyfitted to the input piston 194. Specifically, in the middle of the inputpiston 194, a slide hole 203 that slidably fits the rear end of theguide shaft 202, and a bottomed hole 204 having a larger diameter thanthe slide hole 203, a front end connected to a rear portion of the slidehole 203, and a closed rear end are coaxially provided. The rear end ofthe guide shaft 202 protrudes into the bottomed hole 204 according toforward movement of the input piston 194 relative to the guide shaft202.

A plurality of through holes 205 that provide communication between therelease chamber 132 that the front surface of the end wall 66 a facesand the stroke fluid chamber 193 are bored in the end wall 66 a of thefront end of the control piston 66 with the same distance from thecenter of the control piston 66. The working fluid is introduced intothe stroke fluid chamber 193 in the control piston 66 via the throughholes 205.

The through holes 205 are closed by the seat stopper 135 secured to thebackup piston 64 when the control piston 66 advances by a predeterminedadvance stroke or more. The seat stopper 135 includes: a retainer 206secured to the backup piston 64 so as to abut against the inward flange64 d by press-fitting an outer periphery thereof into the innerperiphery the rear small diameter portion 64 b in the backup piston 64;and an elastic seal member 207 held by the retainer 206.

In FIG. 9, the retainer 206 integrally includes: a ring plate 206 a thatabuts against the inward flange 64 d from behind, an inner cylindricalportion 206 b having a cylindrical shape surrounding the extendedcylindrical portion 68 b of the second reaction piston 68 and having afront end connected to an inner periphery of the ring plate 206 a, andan outer cylindrical portion 206 c having a cylindrical shape coaxiallysurrounding the inner cylindrical portion 206 b and having a front endconnected to an outer periphery of the ring plate 206 a, and is made ofmaterial having a rigidity such as metal, and has a ring shape. Theouter cylindrical portion 206 c is press-fitted into the backup piston64 so as to form an annular minute gap 208 between the extendedcylindrical portion 68 b and the inner cylindrical portion 206 b.

An elastic seal member 207 includes inner and outer cylindrical lips 207a and 207 b so as to come into contact with the front surface of the endwall 66 a on inner and outer sides of the through holes 205 radially ofthe control piston 66 and closes the through holes 205. The elastic sealmember 207 is inserted between the inner cylindrical portion 206 b andthe outer cylindrical portion 206 c, and bonded to the retainer 206 bybaking. Part of the lips 207 a and 207 b protrude from the retainer 206toward the control piston 66 in a normal state in which the end wall 66a of the control piston 66 does not abut against the lips.

Further, when the control piston 66 further advances from a state wherethe lips 207 a and 207 b of the elastic seal member 207 come intocontact with the end wall 66 a, the inner cylindrical portion 206 b andouter cylindrical portion 206 c in the retainer 206 abut against thefront surface of the end wall 66 a outside the elastic seal member 207and can obtain a metal touch. As a result, the outer cylindrical portion206 c comes into contact with the front surface of the end wall 66 aradially outward of the lips 207 a and 207 b in contact with the frontsurface of the end wall 66 a on the inner and outer sides of the throughholes 205 radially of the control piston 66, and the inner cylindricalportion 206 b comes into contact with the front surface of the end wall66 a radially inward of the lips 207 a and 207 b.

In a rear surface of the retainer 206, that is, outer surfaces of thering plate 206 a and the outer cylindrical portion 206 c, acommunication groove 209 is provided for communication between the innerside of the retainer 206 and a portion of the release chamber 132outside the control piston 66 with the end wall 66 a of the controlpiston 66 coming into contact with the lips 207 a and 207 b of theelastic seal member 207.

Specifically, in a state in which the end wall 66 a of the controlpiston 66 is in contact with the lips 207 a and 207 b of the elasticseal member 207, also the extended cylindrical portion 68 b of thesecond reaction piston 68 comes into contact with the end wall 66 a, aportion between the retainer 206 and the extended cylindrical portion 68b communicates with the portion of the release chamber 132 outside thecontrol piston 66 via the minute gap 208 and the communication groove209; and in a state in which the end wall 66 a of the control piston 66is in contact with the elastic seal member 207, negative pressure is notgenerated in a space that the rear portion of the retainer 206 facesinward of the elastic seal member 207 according to the retraction of thecontrol piston 66, and atmospheric pressure is maintained.

Returning to FIG. 6, the control piston 66 has a bottomed cylindricalshape with part of the inner peripheral surface thereof being a taperedsurface 210 with a diameter decreasing toward the front forward of theinput piston 194. In this embodiment, a front half of the control piston66 is formed as a tapered cylindrical portion 66 b with the innerperipheral surface being the tapered surface 210.

The slide member 201 is slidably housed in the control piston 66 forwardof the tapered surface 210. The elastic body 199 mounted between theslide member 201 and the input piston 194 has a cylindrical shape so asto be elastically deformed according to the action of an axialcompressive force along with the advance of the input piston 194, andprevented from being deformed sequentially from the front by restraintwith the tapered surface 210 according to an increase in the axialcompressive force, and the cylindrical shape has the same outer diameteralong the axial length thereof in a non-acting state of the load.

The guide shaft 202 fitted to the input piston 194 so that the rear endthereof is supported by the input piston 194 has a cylindrical shape anda coaxial release passage 211 along the axial length thereof. In theinput piston 194, a plurality of passages 212 having inner ends openinginto the bottomed hole 204 communicating with the release passage 211are provided radially of the input piston 194 forward of a portion towhich the seal member 198 is mounted. Thus, the passages 212 and thebottomed hole 204 provide communication between the portion between theelastic body 199 and the control piston 66, and the release passage 211of the guide shaft 202 in the stroke fluid chamber 193.

A release passage 213 coaxially connected to the front end of therelease passage 211 is provided in the slide member 201. A plurality ofgrooves 214 for preventing the release passage 213 from being closed bythe end wall 66 a when the slide member 201 abuts against the end wall66 a of the front end of the control piston 66 are radially provided ina front end surface of the slide member 201.

With such a configuration, until the through holes 205 are closed by theseat stopper 135 at the time of advance of the control piston 66 and thestroke fluid chamber 193 enters a fluid pressure lock state, a portionbetween the elastic body 199 in the control piston 66 and the controlpiston 66 communicates with the release chamber 132 via the passages212, the bottomed hole 204, the release passages 211 and 213, the groove214, and the through holes 205. Specifically, the portion between theelastic body 199 and the control piston 66 communicates with the releasechamber 132, that is, the reservoir 31, in an advance stroke of thecontrol piston 66 until the working fluid is sealed in the controlpiston 66.

A rear end of a boot 215 that covers a protruding portion of the controlpiston 66 from the body 17 is mounted to the input rod 197 connected tothe brake pedal 11, and a front end of the boot 215 is mounted to therear end of the body 17. Further, a release passage 216 that providescommunication between the inside of the boot 215 and the outside isprovided in the rear end of the body 17

Next, an operation of the embodiment will be described. In the tandemtype master cylinder M, the rear master piston 23 having the rearsurface facing the booster fluid pressure generation chamber 22, and thefront master piston 24 that forms the rear output fluid pressure chamber25 with the rear master piston 23 and has the front surface facing thefront output fluid pressure chamber 26 are slidably housed in thecylinder body 16. The short cylindrical separator 18, the cylindricalfirst sleeve 19 that forms the channel 94 with the separator 18 and isplaced backward of the separator 18, and the stepped cylindrical secondsleeve 20 placed backward of first sleeve 19 are fluid-tightly fittedand secured to the body 17 connected to the cylinder body 16 so as toconstitute the casing 15 with the cylinder body 16. The backup piston 64that can directly presses the rear master piston 23 at the time ofreduction in the fluid pressure in the fluid pressure generation source12 forms the annular passage 93 communicating with the channel 94 withthe inner periphery of the first sleeve 19 and is slidably fitted to theseparator 18, the first sleeve 19, and the second sleeve 20. The O ring95 that seals the front side of the annular passage 93 is mounted to theinner periphery of the separator 18 so as to come into repulsive contactwith the outer periphery of the backup piston 64, and the O ring 96 thatseals the rear side of the annular passage is mounted to the outerperiphery of the backup piston 64 so as to come into repulsive contactwith the inner periphery of the first sleeve 19.

Thus, even if the backup piston 64 advances so as to directly press therear master piston 23, the O ring 95 that seals between the backuppiston 64 and the separator 18 is not moved, thereby allowing an axiallength of the separator 18 to be reduced and allowing an axial length ofthe casing 15 to be reduced to contribute to reduction in the entireaxial length of the vehicle braking device.

The first sleeve 19 has the larger inner diameter than the separator 18and the same inner diameter over the entire axial length thereof. Thebackup piston 64 includes: the front small diameter portion 64 a thatforms the annular passage 93 with the inner periphery of the firstsleeve 19 and is slidably fitted to the separator 18; and the middlelarge diameter potion 64 c that has the larger diameter than the frontsmall diameter portion 64 a and is slidably fitted to the first sleeve19, and has the stepped cylindrical shape, thereby easily forming theannular passage 93.

The annular recess 86 that opens the inner end of the connection port77, the annular recess 87 that opens the inner end of the input port 78,and the annular recess 88 that opens the inner end of the output port 79are provided in the inner periphery of the body 17, and the O rings 89,90, 91, and 92 that seal the annular recesses 86, 87, and 88 from theopposite sides are mounted to the outer peripheries of the cylinder body16 of the master cylinder M, the separator 18, the first sleeve 19, andthe outer periphery of the second sleeve 20. The spaces L1 and L2between the front edges of the annular recesses 86 to 88 in the fittingdirection of the separator 18, the first sleeve 19, and the secondsleeve 20 into the body 17 are set to values that prevent the pluralityof O rings 90 to 92 from simultaneously passing through the front edgeswhen the separator 18, the first sleeve 19, and the second sleeve 20 arefitted into the body 17. In the embodiment, the space L1 between thefront edges of the annular recesses 86 and 87 is set to the smallervalue than the space L3 between the O rings 90 and 91, and the space L2between the front edges of the annular recesses 87 and 88 is set to thesmaller value than the space L4 between the O rings 91 and 92.

Such setting of the spaces L1 to L4 prevents two or more O rings amongthe three O rings 90 to 92 from simultaneously passing through theplurality of front edges in the fitting direction of the annularrecesses 86 to 88, when the separator 18, the first sleeve 19, and thesecond sleeve 20 are fitted and assembled to the body, eliminates theneed for a large force for fitting of the separator 18, the first sleeve19, and the second sleeve 20, and allows the separator 18, the firstsleeve 19, and the second sleeve 20 to be fitted without a large force,thereby preventing damage to the O rings 90 to 92, and facilitatingfitting and assembling of the separator 18, the first sleeve 19, and thesecond sleeve 20 to the body 17 to improve assemblability.

The backup piston 64 is provided in a compressed manner between thesecond sleeve 20 and the retainer 102 mounted to the rear portion of thebackup piston 64, and urged toward the retraction limit that abutsagainst the inward flange 17 a via the stopper 100 by the return spring103 surrounding the rear half of the backup piston 64. The rear returnspring 29 of the master cylinder M does not need to exert a spring forcefor urging the backup piston 64 toward the retraction limit.

Thus, only fluid pressure higher than a relatively small spring force isrequired to act on the booster fluid pressure working chamber 22 foradvancing the rear master piston 23, thereby preventing the delay ofactuation of the master cylinder M in early stages of the brakeoperation. Setting the spring force of the return spring 103 for urgingthe backup piston 64 toward the retraction limit to a relatively largevalue can reliably return the backup piston 64 to the retraction limitafter the actuation.

The control piston 66 included in the fluid pressure booster 13 isformed separately from the backup piston 64 so as to abut against,press, and actuate the backup piston 64 at the time of reduction in thefluid pressure in the booster fluid pressure generation chamber 121, andthus tolerance from the front end of the backup piston 64 to the rearend of the control piston 66 can be absorbed to improve theassemblability. The front end of the backup piston 64 at the retractionlimit abuts against the rear master piston 23 in the non-operation stateof the brake pedal 11, and thus tolerance at the time of assembling ofthe backup piston 64 itself to the fluid pressure booster 13 iscontrolled to eliminate the need for adjusting an invalid stroke whenthe fluid pressure booster 13 and the master cylinder M are connected,thereby further improving the assemblability.

Further, the front end of the backup piston 64 abuts against the entireperipheral edge of the rear surface of the rear master piston in thenon-operation state of the brake pedal 11, thereby ensuring smoothactuation of the rear master piston 23 by pressing the backup piston 64.

Further, the passage 139 that leads the fluid pressure from the fluidpressure booster 13 to the front end of the backup piston 64 and therear surface of the rear master piston are formed between abuttingportions of the front end of the backup piston 64 and the rear surfaceof the rear master piston 23, so that the booster fluid pressure can beeasily caused to act on the entire rear surface of the rear masterpiston 23 in the abutting state of the backup piston 64. The groove 140that forms the passage 139 with the front end of the backup piston 64 isprovided in the rear surface of the rear master piston 23, and thus thepassage 139 can be easily formed between the front end of the backuppiston 64 and the rear surface of the rear master piston 23.

The long through hole 44 is provided in the rear master piston 23 alongone diameter line of the rear master piston 23 and along the axis of therear master piston 23. The master cylinder M is of the center valve typeso that the stopper pin 43 secured to the cylinder body 16 is insertedinto the through hole 44, the groove 140 is provided in the rear surfaceof the rear master piston 23 in parallel with the axis of the throughhole 44, and thus the groove 140 formed in the rear surface of the rearmaster piston 23 can be used for positioning at the time of insertingthe rear master piston 23 into the cylinder body 16, thereby improvingthe assemblability.

The booster fluid pressure generated in the fluid pressure booster 13 isonce taken out of the body 17 and then guided to the booster fluidpressure working chamber 22 in the cylinder body 16. The passage 137 isformed between the rear end of the cylinder body 16 and the separator 18so as to provide communication between the annular recess 86communicating with the connection port 77 to which the booster fluidpressure from the fluid pressure booster 13 is led and the booster fluidpressure working chamber 22, thereby simplifying a passage structure forleading the booster fluid pressure from the outside of the cylinder body16 and the body 17 into the booster fluid pressure working chamber 22.Further, the separator 18 abuts against the rear end of the cylinderbody 16, and the passage 137 is constituted by the groove 138 providedin the rear end of the upper portion of the cylinder body 16 and theseparator 18, so that specifying the upper position of the cylinder body16 with the groove 138 facilitates assembling of the cylinder body 16and the body 17, and increases air venting properties of the boosterfluid pressure working chamber 22.

The fluid pressure booster 13 includes: the control piston 66 in whichthe brake operation input from the brake pedal 11 acts in the advancingdirection, and the reaction based on the fluid pressure in the boosterfluid pressure generation chamber 121 acts in the retracting direction;the pressure increasing valve 106 provided between the booster fluidpressure generation chamber 121 and the input chamber 113 communicatingwith the fluid pressure generation source 12 so as to open at the timeof the advance of the control piston 66 and close at the time of theretraction of the control piston 66; and the pressure reducing valve 107provided between the release chamber 132 communicating with thereservoir 31 and the booster fluid pressure generation chamber 121 so asto close at the time of the advance of the control piston 66 and open atthe time of the retraction of the control piston 66. The fluid pressurebooster 13 is built in the backup piston 64. The pressure increasingvalve 106 includes the first and second valve means 141 and 142 thatsequentially opens according to the increase in the brake operationinput, and the seal diameter of the second valve means 142 is largerthan the seal diameter of the first valve means 141.

Thus, in the early stages of the brake operation requiring small brakeoperation input, initial response can be ensured by opening the firstvalve means 141 having a small activation load (a force required foropening the valve), and response can be increased by opening both thefirst and second valve means 141 and 142 when the brake pedal 11 isstrongly operated, thereby enhancing the initial response of thepressure increasing valve 106 as well as the response of the pressureincreasing valve 106 when the brake pedal 11 is strongly operated.

The first and second valve means 141 and 142 are axially arranged sideby side along the axis of the control piston 66, and thus the pressureincreasing valve 106 including the first and second valve means 141 and142 can be made compact, and the second valve means 142 is configured tostart opening before the rate of flow from the opened first valve means141 reaches maximum. Thus, as shown in FIG. 10, the second valve means142 opens after the first valve means 141 opens according to the advanceof the pressing rod 149 and before the rate of flow from the first valvemeans 141 reaches maximum, and thus the first and second valve means 141and 142 continuously smoothly open according to the increase in thebrake operation input, thereby preventing a feeling of stepped strokeand providing a good operation feeling.

The first valve means 141 of the pressure increasing valve 106 includes:the slide member 144 that constitutes at least part of the insertedmeans 156 inserted into the backup piston 64 and supported and has thefirst valve seat 143; the retainer 146 that forms the valve chamber 145that communicates with the fluid pressure generation source 12 and thatthe first valve seat 143 faces, and is mounted to the valve seat member117 of the inserted means 156; the valve body 147 that can be seated onthe first valve seat 143 and is slidably fitted to the retainer 146; thefirst valve spring 148 that urges the valve body 147 to be seated on thefirst valve seat 143 and is provided between the retainer 146 and thevalve body 147; and the pressing rod 149 that can abut against the valvebody 147, cooperates with and is connected to the control piston 66, andis inserted into the slide member 144 movably in the axial direction.

With such a configuration of the first valve means 141, the slide member144 that constitutes part of the inserted means 156 before beinginserted into the backup piston 64 has the first valve seat 143, thevalve body 147 is housed in the valve chamber 145 in the retainer 146mounted to the inserted means 156, the first valve spring 148 isprovided between the valve body 147 and the retainer 146, and thepressing rod 149 is inserted into the slide member 144, therebyassembling the components of the pressure increasing valve 106 to theinserted means 156, and improving the assemblability of the pressureincreasing valve 106.

The communication holes 165 that provide communication between the inputchamber 113 communicating with the fluid pressure generation source 12and the valve chamber 145 are provided in the side wall of the retainer146 so as to be placed on the opposite side of the valve body 147relative to the seating position of the valve body 147 on the firstvalve seat 143. Thus, the high pressure working fluid flowing from thecommunication holes 165 into the valve chamber 145 does not flow alongthe side of the valve body 147 toward the first valve seat 143, therebypreventing the valve body 147 from being engulfed by the flow of theworking fluid, and improving seating properties of the valve body 147.

The second valve means 142 includes: the valve portion 150 provided inthe slide member 144 that is the common component shared with the firstvalve means 141; the valve seat member 117 that has the second valveseat 151 on which the valve portion 150 can be seated and slidably fitsthe slide member 144; the retainer 146 that is the common componentshared by the first valve means 141; and the second valve spring 152that urges the valve portion 150 to be seated on the second valve seat151 and is provided between the retainer 146 and the slide member 144.The pressing rod 149 common to the first and second valve means 141 and142 is formed to press the slide member 144 so that the valve portion150 is separated from the second valve seat 151 after the opening of thefirst valve means 141 at the time of increase in the brake operationinput.

Specifically, although the pressure increasing valve 106 has a valvestructure that opens in two stages, the slide member 144, the retainer146, and the pressing rod 149 are common to the first and the secondvalve means 141 and 142, thereby reducing the increase in the number ofcomponents to provide a compact configuration.

Further, the axially-extending flow grooves 161 each having one endcommunicating with the valve chamber 145 and the other end communicatingwith the booster fluid pressure generation chamber 121 when the valveportion 150 is separated from the second valve seat 151 in the secondvalve means 142 are provided in the inner surface of the valve seatmember 117. The slide hole 160 and the plurality of flow grooves 161 inthe valve seat member 117 form the flow passage 162, thus the workingfluid can be caused to flow from the valve chamber 145 into the boosterfluid pressure generation chamber 121 through the flow passage 162 atthe time of opening of the second valve means 142, so that a sufficientflow rate of working fluid can be ensured without increasing the innerperipheral diameter of the valve seat member 117, that is, withoutincreasing the size of the fluid pressure booster 13. Further, at thetime of opening of the first valve means 141, the working fluid flowingfrom the valve chamber 145 into the annular chamber 163 flows throughthe flow passage 162 toward the booster fluid pressure generationchamber 121 via the communication hole 164, so that flow resistance canbe also reduced at the time of opening of the first valve means 141 toallow the working fluid of the valve chamber 145 to flow toward thebooster fluid pressure generation chamber 121.

The pressing rod 149 is slidably fitted to the middle of the disk-shapedrectifying member 168 that can abut against the surface facing thebooster fluid pressure generation chamber 121 of the valve seat member117 to close the open end of the flow passage 162 opening into thebooster fluid pressure generation chamber 121. The rectifying member 168whose axial movement is guided only by the pressing rod 149 is urgedtoward the valve seat member 117 by such a spring force as to separatethe rectifying member 168 from the valve seat member 117 according tothe fluid pressure from the fluid pressure generation source 12, thatis, from the input chamber 113 acting on the flow passage 162. When thehigh pressure working fluid from the fluid pressure generation source 12flows through the flow passage 162 into the booster fluid pressuregeneration chamber 121 along with the opening of the pressure increasingvalve 106, the working fluid pushes away the rectifying member 168 so asto be separated from the valve seat member 117 to rectify the flow,thereby suppressing generation of operation noise or pulsing caused bythe opening of the pressure increasing valve 106. Further, the axialmovement of the rectifying member 168 is guided only by the pressing rod149 that is slidably fitted to the middle of the rectifying member 168,thereby preventing resistance or catching in the axial movement of therectifying member 168 to ensure smooth actuation of the rectifyingmember 168.

A pressure receiving area facing the flow passage 162 of the rectifyingmember 168 is changed to change valve opening pressure of the rectifyingmember 168, thereby increasing the degree of freedom in design. Further,the surface of the rectifying member 168 facing the flow passage 162 isthe flat surface 168 a, and thus the inner diameter or the shape of theflow passage 162 is simply changed to change the valve opening pressureof the rectifying member 168, thereby further increasing the degree offreedom in design.

The first reaction piston 67 is coaxially connected to the controlpiston 66 so that the fluid pressure in the booster fluid pressuregeneration chamber 121 acts in the retracting direction, and the firstreaction piston 67 is fitted to the second reaction piston 68 relativelyslidably in the axial direction. The release passage 178 communicatingwith the booster fluid pressure generation chamber 121 at the time ofopening of the pressure reducing valve 107 is provided in the firstreaction piston 67, and the release passage 178 is connected to therelease chamber 132, through the temporary storage chamber 180 thattemporarily stores the working fluid from the release passage 178 andthrough the orifice 181 that is provided between the release chamber 132that the front surface of the control piston 66 faces and thatcommunicates with the reservoir 31 and the temporary storage chamber180.

Thus, when the high pressure in the booster fluid pressure generationchamber 121 is released to the release chamber 132 along with theopening of the pressure reducing valve 107, the working fluid flows fromthe release passage 179 provided in the first reaction piston 67 to therelease chamber 132 via the temporary storage chamber 180 and theorifice 181, so that the fluid pressure of the working fluid temporarilystored in the temporary storage chamber 180 is narrowed by the orifice181, thereby slowly releasing the high fluid pressure toward the releasechamber 132 to prevent generation of operation noise.

The steps 67 b and 68 c facing each other are provided in the outerperiphery of the first reaction piston 67 and the inner periphery of thesecond reaction piston 68, and the temporary storage chamber 180 has thering shape surrounding the first reaction piston 67 between the steps 67b and 68 c, so that the temporary storage chamber 180 can be easilyformed.

Further, the orifice 181 is formed by setting the annular gap by theamount of the tolerance between the outer periphery of the firstreaction piston 67 and the inner periphery of the second reaction piston68, so that the orifice 181 can be easily formed.

The stroke simulator 14 includes the elastic body 199 made of theelastic material and the metal coil spring 200 having the smaller springconstant than the elastic body 199, which are connected in seriesbetween the input piston 194 and the control piston 66 connected to thebrake pedal 11 so that the elastic deformation of the elastic body 199is started after the completion of the action of the spring forceexerted by the coil spring 200 in the early stages of the brakeoperation on the control piston 66. The coil spring 200 has the lowerset load than other springs 134 connected to the coil spring 200 inseries so as to exert the forward and backward spring forces.

Thus, the load from the coil spring 200 previously acts on the elasticbody 199, and even if the elasticity of the elastic body 199 isdeteriorated, the coil spring 200 absorbs the deterioration to eliminatethe invalid stroke at the time of normal braking, and two stageoperation simulating properties by the elastic body 199 and the coilspring 200 can be obtained irrespective of the deterioration of theelastic body 199. Further, in the early stages of the brake operation,the coil spring 200 of the stroke simulator 14 is deformed to obtain theinvalid stroke, and relatively small brake operation input is applied inthe early stages of the brake operation to improve the operationfeeling.

The control piston 66 has the cylindrical shape with part of the innerperipheral surface thereof being the tapered surface 210 with thediameter decreasing toward the front. The elastic body 199 of the strokesimulator 14 is axially slidably housed in the control piston 66backward of the tapered surface 210 while being mounted between theinput piston 194 connected to the brake pedal 11 and the control piston66. The elastic body 199 is elastically deformed according to the actionof the axial compressive force along with the advance of the inputpiston 194, and is prevented from being deformed sequentially from thefront by the restraint with the tapered surface 210 according to theincrease in the axial compressive force.

Specifically, when the input piston 194 advances according to the brakeoperation of the brake pedal 11, the coil spring 200 is compressed toincrease the stroke in proportion to the input load until the advancestroke reaches S1 as shown in FIG. 11. Then, when the input piston 194advances while axially compressing the elastic body 199, the elasticbody 199 is elastically deformed according to the axial compression, butthe elastic deformation of the elastic body 199 is sequentiallyprevented from the front by the restraint with the tapered surface 210of the control piston 66 according to the increase in the axialcompressive force, thereby increasing the amount of change in the inputload relative to the operation stroke of the brake pedal 11. On theother hand, when the brake operation force by the brake pedal 11 isreleased, elastic energy increased by the restraint with the taperedsurface 210 acts on the brake operation pedal 11 in the returningdirection in a state in which the elastic deformation of the elasticbody 199 is prevented by the restraint. Thus, a relationship between thebrake operation stroke and the operation load in the stroke simulator 14can have a nonlinear characteristic and a large hysteresis width,thereby reducing an operation load on a driver. This provides anoperation feeling equivalent to that of a general vehicle braking deviceincluding a combination of a master cylinder, a negative pressurebooster, and a wheel brake, and reduces uncomfortable feelings for thedriver.

The elastic body 199 has the cylindrical shape with the same outerdiameter along the axial length thereof in the non-acting state of theload, thereby simplifying the shape of the elastic body 199 tofacilitate molding of the elastic body 199, and preventing generation ofoffset loads on the elastic body 199 to increase durability of theelastic body 199.

The working fluid is introduced into the control piston 66, and theportion between the elastic body 199 and the control piston 66communicates with the reservoir 31 in the advance stroke of the controlpiston 66 until the working fluid is sealed in the control piston 66.This prevents the working fluid in the control piston 66 from beinglocked between the elastic body 199 and the control piston 66 before thecontrol piston 66 reaches a predetermined advance stroke, allowing theelastic body 199 to reliably abut against the inner peripheral surfaceof the control piston 66 to obtain desired hysteresis, and preventingimpairment of operability.

The cylindrical guide shaft 202 coaxially having the release passage 211that provides communication between the portion between the elastic body199 and the control piston 66 and the reservoir 31, and passes throughthe elastic body 199 is supported by the input piston 194, that is, therelease passage 211 can be formed with a simple configuration.

The control piston 66 has the bottomed cylindrical shape, and has, atthe front end thereof, the end wall 66 a having the front surface thatfaces the release chamber 132 communicating with the reservoir 31 and isformed in the backup piston 63 and the through holes 205, the inputpiston 194 forms the stroke fluid chamber 193 with the end wall 66 a andis fluid-tightly and slidably fitted to the control piston 66, and theelastic seal member 207 that closes the through holes 205 in the advancestroke with a predetermined amount or more of the control piston 66 isheld by the retainer 206 having rigidity and pressed into the backuppiston 64. Thus, when the through holes 205 in the front end of thecontrol piston 66 are closed in the advance stroke of the predeterminedamount or more of the control piston 66, the stroke fluid chamber 193 issealed to prevent movement of the input piston 194 relative to thecontrol piston 66 in the advancing direction, thereby suppressing theincrease in the stroke and the reaction of the brake pedal 11 that aremade invalid by the stroke simulator 14 at the time of failure of thefluid pressure generation source 12. Further, the structure for sealingthe working fluid in the control piston 66 in the advance stroke of thepredetermined amount or more of the control piston 66 is simplified, andfurther the elastic seal member 207 is held by the retainer 206 havingthe rigidity and pressed into the backup piston 64, thereby facilitatingassembling of the retainer 206, that is, the elastic seal member 207 tothe backup piston 64.

The elastic seal member 207 is bonded to the metal retainer 206 bybaking, thereby enhancing sealability of the elastic seal member 207 tothe retainer 206.

Further, the end wall 66 a has the plurality of through holes 205 toallow the working fluid to flow between the stroke fluid chamber 193 andthe release chamber 132 with good response according to the actuation ofthe input piston 194, and the ring-shaped elastic seal member 207 thatcan close the through holes 205 in common is held by the ring-shapedretainer 206, thereby allowing the plurality of through holes 205 to beclosed by the single elastic seal member 207 to reduce the number ofcomponents. Further, the communication groove 209 is provided in therear surface of the retainer 206 so as to provide communication betweenthe inner side of the retainer 206 and the portion of the releasechamber 132 outside the control piston 66 in a state in which theelastic seal member 207 is in contact with the end wall 66 a. Thus, theinner side of the retainer 206 is at atmospheric pressure with thethrough holes being closed by the elastic seal member 207, therebypreventing any difference in pressure between the front and rear of theretainer 206 when the control piston 66 is retracted from the state ofcontact with the elastic seal member 207, and preventing the differencein pressure from causing an unstable state of the retainer 206 securedto the backup piston 64.

Further, the retainer 206 that holds the elastic seal member 207 canabut against the front surface of the end wall 66 a outside the elasticseal member 207 to obtain a metal touch, and a protrusion of the elasticseal member 207 from the retainer 206 or erosion caused by theprotrusion is prevented to increase sealability when the working fluidis sealed in the control piston 66 in the advance stroke of thepredetermined amount or more of the control piston 66.

The embodiment of the present invention has been described above, butthe present invention is not limited to the embodiment, and variouschanges in design may be made without departing from the presentinvention described in claims.

For example, in the embodiment, the fluid pressure booster for boostingthe tandem type master cylinder M has been described, but the presentinvention may be applied to a fluid pressure booster for boosting amaster cylinder in which a single master piston is slidably housed in acasing.

1. A fluid pressure booster comprising: a control piston in which brakeoperation input from a brake operation member acts in an advancingdirection, and reaction based on fluid pressure of a booster fluidpressure generation chamber that generates fluid pressure for actuatinga master piston of a master cylinder acts in a retracting direction; apressure increasing valve provided between the booster fluid pressuregeneration chamber and a fluid pressure generation source so as to openat the time of advance of the control piston and close at the time ofretraction of the control piston; and a pressure reducing valve providedbetween a release chamber communicating with a reservoir and the boosterfluid pressure generation chamber so as to close at the time of theadvance of the control piston and open at the time of the retraction ofthe control piston, the control piston being actuated forward andbackward so that the brake operation input and the reaction based on thefluid pressure in the booster fluid pressure generation chamber arebalanced to aregulate the fluid pressure in the fluid pressuregeneration source to act on the booster fluid pressure generationchamber, wherein the pressure increasing valve includes first valvemeans and second valve means that sequentially open according to anincrease in the brake operation input, and a seal diameter of the secondvalve means is larger than that of the first valve means.
 2. The fluidpressure booster according to claim 1, wherein the first valve means andthe second valve means are arranged side by side along the axis of thecontrol piston.
 3. The fluid pressure booster according to claim 1,wherein the second valve means starts opening before a rate of flow fromthe first valve means reaches maximum.
 4. The fluid pressure boosteraccording to claim 2, wherein the second valve means starts openingbefore a rate of flow from the first valve means reaches maximum.